The present invention relates to bearing structures for use in a rotational structure of a mechanical structure and in an automobile cabin and further relates to a seat weight measuring apparatus having the bearing structures. In particular, it relates to a rotational structure and a bearing structure wherein discomfort of people therearound is eliminated by suppressing noise due to movement (rattle) of a member in a rotational supporting point within small clearance.
In an automobile cabin, various bearing structures are used, in which shaft members are inserted into bearing members. In these bearing structures, rattling of the shaft member may occur due to errors in size of the shaft member, the bearing member, and a sleeve member, or errors in size of a vehicle cabin and a seat. Although noise due to the chattering is very low, comfortableness in the automobile cabin may be reduced. Therefore, means for suppressing the rattle of the bearing structures is required.
The prior art will be described in detail below with reference to the bearing structure in the automobile cabin as an example, in which a seat belt and an airbag are equipped.
With regard to the current trend, in order to improve the performance of the seat belt and the airbag, operation of such safety equipment may be controlled in accordance with the weight of an occupant. For example, the gas quantity or gas rate for deploying the airbag may be adjusted, or the pre-tension of the seat belt may be adjusted according to the weight of an occupant. That requires detecting the weight of an occupant. As an example of such means, it is proposed to measure the seat-weight including the weight of an occupant by arranging load sensors (load cells) at four corners, back-and-forth and the right and left, under the seat so as to sum the loads applied to the load cells in the vertical direction.
An example of such a seat-weight measuring apparatus is disclosed in Japanese Unexamined Patent Application Publication No. 2000-258233 (incorporated by reference herein in its entirety). The seat-weight measuring apparatus in the Publication simply measures not only the weight of an occupant and a seat but also has a mechanism for absorbing displacement and/or deflection between the seat and a vehicle body for eliminating the load other than from the weight of the seat and an occupant (or goods) thereon as much as possible. In the seat-weight measuring apparatus having such a deflection absorbing mechanism, bearing structures are also used, so that means for suppressing rattle of bearing parts is also required.
Referring to FIGS. 9 to 12, the seat-weight measuring apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2000-258233 will be further described below. First, structures around an vehicle seat will be described with reference to FIG. 12.
FIG. 12(A) is a front sectional view for schematically showing a structure of the seat attached to the vehicle body; and FIG. 12(B) is a side view thereof. In addition, arrows shown in the drawings indicate the following directions. UP: upward gravitational direction when the vehicle body is horizontal, DOWN: downward direction, FRONT: vehicle proceeding direction, REAR: reverse travel direction, LEFT: the left side facing in the vehicle proceeding direction, and RIGHT: the right side.
In FIGS. 12(a) and 12(b), a seat 3 is shown. An occupant 1 sits on a seat cushion 3a. The bottom surface of the seat cushion 3a is supported by a seat frame 5 made of a steel plate. The seat frame 5 comprises a bottom plate 5a, side plates 5c, vertical plates 5e, and slide plates 5g. The bottom plate 5a spreads out so as to cover the bottom surface of the seat cushion 3a. The side plates 5c extend along the respective right and left sides of the bottom surface of the bottom plate 5a. The vertical plate 5e hangs down from the bottom surface center of the side plate 5c. The slide plate 5g protrudes to the right and left from the vertical plate 5e as blades, and end portions thereof are further bent upwardly.
Two seat rails 7 are arranged in parallel under the seat 3 in the right and left sides, extending in the back-and-forth direction. The cross-section of the seat rail 7 is U-shaped, a concave portion 7c exists inside thereof. The upper opening of the concave portion 7c is a groove 7a extending in the back-and-forth direction. Into the groove 7a, the vertical plate 5e of the seat frame 5 is inserted. Into the concave portion 7c of the seat rail 7, the slide plate 5g of the seat frame 5 is entered. The slide plate 5g is slidable within the seat rail 7 in the back-and-forth direction. To the bottom surface of the seat rail 7, the seat-weight measuring apparatus 9 is connected. The seat-weight measuring apparatus 9 has an elongated box-like shape extending in the back-and-forth direction. Details of the seat-weight measuring apparatus 9 will be described later. At the front and rear ends of the bottom surface of the seat-weight measuring apparatus 9, seat brackets 11 are attached. The seat bracket 11 is fixed to a seat fixing portion 13 of the vehicle body with bolts, etc.
Next, the structure of the seat-weight measuring apparatus is described.
FIG. 9(A) is a disassembled perspective view of the displacement and/or deflection absorbing mechanism of the seat-weight measuring apparatus 9; FIG. 9(B) is a front sectional view of a pin bracket.
FIG. 10(A) is a plan view of the entire structure of the seat-weight measuring apparatus; FIG. 10(B) is a side sectional view; FIGS. 10(C) and (D) are front sectional views. In addition, in FIGS. 10(A) and (B), substantially half of the rear part is not shown.
FIG. 11(A) is a plan view showing the relationship between a sensor plate and a half arm; FIG. 11(B) is a side view in a no-load state; FIG. 11(C) is a side view schematically showing a state in that a load is applied.
The seat-weight measuring apparatus 9 is constructed based on an elongated rail-like base (base frame) 21. The base 21 extends in the back-and-forth direction when attached to the vehicle body and is a steel-plate pressed product having an upward U-shape front-section as shown in FIGS. 10(C) and (D). The sectional bottom portion of the base 21 is called a bottom plate 21c; portions elevated at right angles from lateral ends of the bottom plate 21c are called side plates 21a. 
In the base side plate 21a, pin holes 21e and 21g are formed two each on the front and rear portions. The respective holes 21e and 21g are formed on the right and left side plates 21a and 21axe2x80x2 opposing each other.
The holes 21e, which are closer to the end, are formed at positions approaching the center by approximately xe2x85x9 of the entire length of the base 21 from the front and rear ends. The hole 21e is a hole much elongated in the vertical direction, as shown in FIG. 9(A). Within the elongated holes 21e, end portions of a bracket pin (stopper pin) 27 are entered.
However, there are clearances between the bracket pin 27 and top/bottom and right/left ends of the elongated hole 21e, so that the bracket pin 27 does not normally come into contact with internal edges of the elongated hole 21e. When an excessive load is applied to the seat-weight measuring apparatus 9 (specifically, part of a pin bracket 25), however, the bracket pin 27 is lowered and abuts the bottom end of the elongated hole 21e, so that the excessive load cannot be transmitted to a load sensor (a sensor plate 51, details will be described). That is, the pin 27 and the elongated hole 21e form part of a mechanism for restricting the upper limit load applied to the sensor plate 51. In addition, the principal function of the bracket pin 27 is to transmit the seat weight applied to the pin bracket 25 to a Z-arm (arm member) 23.
At positions slightly closer to the center from the elongated holes 21e (approaching the center by approximately {fraction (1/10)} of the entire length of the base 21), the pin holes 21g are formed. Into the pin holes 21g, a base pin (pivot pin) 31 is inserted. The base pin 31 exists so as to bridge between the right and left base side plates 21a and 21axe2x80x2. At lateral ends of the pin 31, retainers 33 are attached, so that the base pin 31 is fixed to the base 21. In addition, the base pin 31 is a rotational central axis of the Z-arm 23.
The Z-arm 23 is arranged inside the base 21. The Z-arm 23 has a shape in plan view, in which one end closer to the center of the base 21 is forked into two parts (forked parts 23h) while the other end closer to the front or rear end is rectangular. The lateral ends of the half part closer to the front or rear end are elevated at right angles to form side plates 23a. The forked part 23h is a simple flat plate. The side plate 23a is arranged along the inside of the side plate 21a in the base 21; however, there is a clearance between the side plates 21a and 23a. 
The Z-arm 23 also has two pin holes 23c and 23e formed thereon. Into the pin hole 23c closer to the front or rear end, the bracket pin 27 is inserted. Into the pin hole 23e closer to the center, the base pin 31 is inserted. At the external periphery of the base pin 31 between the base side plate 21a and the Z-arm side plate 23a, a perforated circular disk-like spacer 35 is fitted. The Z-arm 23 is rotated about the base pin 31.
The forked part 23h of the Z-arm 23 has a length approximately half of the entire length of the Z-arm 23. The forked parts 23h are laterally divided and extend toward the center in the front and rear direction, and are reduced in width at portions closer to the center. Application parts 23j at ends of the Z-arm forked parts 23h are sandwiched between blades 41a and 42a of the upper and lower half arms 41 and 42.
When a load is applied to the pin bracket 25, the load is transmitted to the Z-arm 23 via the bracket pin 27 so as to rotate the Z-arm 23 slightly (approximately 5xc2x0 at most), which in turn is transmitted by the application parts 23j to the sensor plate 51 of the load sensor 50 via the half arms 41 and 42.
The pin bracket 25, as shown in FIG. 10(C), has a downward substantially U-shaped cross section. The length thereof in the front and rear direction is not so long, that is, {fraction (1/20)} of that of the base 21. The top part 25a of the pin bracket 25 is flat, and the seat rail 7 shown in FIG. 12 is placed thereon. Both the parts are tightly fixed together with bolts, etc.
Lateral side plates 25b of the pin bracket 25 hang down from sides of the bracket 25, and end portions of the side plates 25b are bent inwardly. The side plates 25b are arranged inside the Z-arm side plates 23a with clearances. On the side plates 25b, pin holes 25c are formed. Into the pin holes 25c, the bracket pin 27 is inserted. The pin holes 25c is larger in size than the diameter of the bracket pin 27. Due to the clearance between them, errors in size of the seat and the vehicle body and accidental deformation are absorbed.
Between the respective lateral side plates 25b and the respective Z-arm side plates 23a, a spring plate 29 is sandwiched. The spring plate 29 has perforated spring-washer portions which are fitted into outsides of the bracket pin 27 with clearances. The spring plate 29 serves as a centering mechanism for urging the pin bracket 25 toward the center.
Such a centering mechanism allows the pin bracket 25 to be positioned in the vicinity of the center of the slidable range as much as possible. Due to the operation of the centering mechanism, the movable ranges of the slide mechanism and the rotational mechanism can be ensured in the both directions (right/left, up/down, and front/rear) after the seat-weight measuring apparatus is equipped.
Next, structures around the sensor plate 51 are described.
The sensor plate (spring member) 51 which is a base material of the load sensor 50 is provided with a strain gauge formed thereon with a bridge circuit having strain resistances 54a to 54d. The sensor plate 51, as shown in FIGS. 10 (A) and (B) and FIG. 11, is tightly fixed to a column 63 in the central portion of the base bottom plate 21c with a washer 67, a nut 68, and a bolt 69.
The half arms 41 and 42, as shown in FIGS. 10 and 11, are components of a group of four, front/rear and up/down, and are assembled so as to sandwich the sensor plate 51 from the front/rear and up/down directions and fixed to sensor plate 51 with bolts 43, etc.
Between both supporting points 41b and 42b of blades 41a and 42a extended from the upper/lower half arms 41 and 42, the application part 23j of the Z-arm 23 is sandwiched. In addition, the supporting points are positioned at just the midpoint (a constricted part 51c of the sensor plate 51) of two strain gauges 54a and 54c or 54d and 54b. 
When a load is applied to the pin bracket 25 of the seat-weight measuring apparatus 9, the Z-arm 23 is slightly rotated so as to raise the application part 23j thereof upwardly. It is FIG. 11(C) to show a state of the sensor plate and the half arm at this time schematically and exaggeratedly.
When the Z-arm application part 23j is raised, the supporting point 41b of the upper half arm 41 is elevated. A moment M is applied to end portions in the back and forth direction of the sensor plate 51. Due to the moment M, the strain gauges 54a and 54b in the end portions in the back and forth direction are pulled while the strain gauges 54c and 54d in the central portion are compressed. Changes in resistance due to these actions of the respective strain gauges are converted to electrical signals so as to measure the strain of the sensor plate and the load applied to the pin bracket 25 by extension.
Next, the entire displacement/deflection absorbing mechanism of the seat-weight measuring apparatus will be described with reference to FIG. 10.
The pin bracket 25 is tightly fixed to the seat rail 7 with bolts, etc. In the vertical direction of the vehicle body, displacement is absorbed by the clearance between the pin hole 25c of the pin bracket 25 and the bracket pin 27.
In the back and forth direction of the vehicle body, the pin hole 25c of the pin bracket 25 is elongated so as to absorb the displacement.
In the right and left direction of the vehicle body, displacement is absorbed by the clearance between the pin bracket side plate 25b and the Z-arm side plate 23a. In addition, the centering mechanism by the spring plate 29 is provided in this part, as described above.
For the rotation about the vertical direction of the vehicle body as the axis, displacement is absorbed mainly by the clearance between the pin bracket side plate 25b and the Z-arm side plate 23a. 
For the rotation about the back and forth direction of the vehicle body as the axis, displacement is absorbed mainly by the clearance between the pin bracket side plate 25b and the Z-arm side plate 23a, just like for about the vertical direction of the vehicle body.
For the rotation about the right and left direction of the vehicle body as the axis, displacement is absorbed mainly by the rotation of the pin bracket 25 about the bracket pin 27.
In the seat-weight measuring apparatus 9 as constructed above, in order to adjust errors in size of each part and prevent strain from being generated, the diameter of the pin hole 23c is slightly larger than that of a bracket pin to be inserted (stopper pin) 27. Therefore, the bracket pin 27 inserted into the pin hole 23c is not rigidly fixed relative to the Z-arm 23. Accordingly, the bracket pin 27 is rattling within the pin hole 23c, so that abnormal noise may be generated due to vibration by vehicle traveling, or the seat rail 7 supported by the bracket pin 27 via the pin bracket 25 may slightly vibrate. Thereby, an occupant sitting on the seat 3 may feel rattle.
The diameter of the pin hole 23e of the Z-arm side plate 23a is also slightly larger than that of the base pin 31 just like mentioned above, the base pin 31 is chattering within the pin hole 23e, so that abnormal noise may be generated due to vibration by vehicle traveling, and comfortableness in a cabin may be damaged.
The present invention has been made in view of these problems, and it is an object of the present invention to provide a rotational structure and a bearing structure wherein discomfort of people therearound can be eliminated by suppressing noise due to movement (rattle) of a member in a rotational supporting point within small clearance. Furthermore, it is another object to provide a seat-weight measuring apparatus having such a rotational structure and a bearing structure.
In order to solve the aforementioned problems, a rotational structure according to the present invention comprises a center-of-rotation pin, two members relatively rotatable about the pin and having insertion holes for the pin, an internal sleeve lying between the insertion hole of one member (a first member) and the external periphery of the pin while extending into the insertion hole of the other member (a second member), and an external sleeve lying between the external periphery of the internal sleeve and the insertion hole of the second member, wherein the internal sleeve, while being press-fitted into the insertion hole of the first member, has a pressing section which is elastically pressed onto the external periphery of the pin so as to slidably and elastically keep the pin in contact with the internal sleeve, and wherein the external sleeve, while being press-fitted into the insertion hole of the second member, has a pressing section which is elastically pressed onto the external periphery of the internal sleeve so as to slidably and elastically keep the internal sleeve in contact with the external sleeve.
According to a rotational structure of the present invention, the free clearance in the radial direction is forced out due to the pressing sections of the external and internal sleeves, so that pins and the external and internal sleeves cannot rattle within insertion holes. Therefore, abnormal noise produced following the chattering of members can be suppressed.
In addition, in the present invention, by contrast to the above description, the bore of the sleeve may be press-fitted so that the pressing section of the sleeve may be elastically urged in the external diameter side, and this case is also within the scope of the present invention.
In a rotational structure according to the present invention, the pressing section may be a tapered end portion of the sleeve.
In this case, the pressing section can be readily fabricated. Moreover, the tapered pressing section fits perfectly on the entire external periphery of the pin or the internal sleeve, the pressing can be performed with a uniform elastic force in the radial direction.
In a rotational structure according to the present invention, the sleeve may have a flange section which lies between side surfaces of the first and second members. In this case, the flange section of the sleeve serves as a plane bearing between the first and second members.
In a rotational structure according to the present invention, a surface of the sleeve may be coated with a material having a low coefficient of friction. In this case, there is an advantage that the sleeve slides more smoothly.
A bearing structure for use in an automobile cabin according to the present invention comprises a bearing member, a sleeve member fitted into an insertion hole of the bearing member, and a shaft member fitted into an insertion hole of the sleeve member, wherein the sleeve member is formed so that any of part of the insertion hole of the sleeve member always comes into contact with the shaft member so as not to allow the shaft member to run freely within the insertion hole of the sleeve member when the shaft member moves.
In the bearing structure according to the present invention, the sleeve member is formed so that any of part of the insertion hole of the sleeve member always comes into contact with the shaft member. Accordingly, the shaft member does not rattle within holes of the sleeve members even when the shaft member moves due to vibration during vehicle traveling, so that noise and vibration are transmitted to the arm member and the sleeve member from the contact portion so as to be damped. Therefore, abnormal noise generated in a cabin during vehicle traveling following the chattering of the shaft member can be suppressed, eliminating uncomfortable feeling of an occupant sitting on the seat.
The bearing structure according to the present invention may also be applied to a seat-weight measuring apparatus. That is, in an apparatus for measuring the seat weight including the weight of an occupant sitting on an automobile seat, the apparatus comprising a rail-like base frame fixed to a vehicle body or part of the seat, an arm member supported to the base frame rotatably in the vertical direction by a pivot member, a stopper pin attached to the arm member and being movably brought into engagement with an opening of the base frame so as to restrict the rotational range of the arm member, and a bracket pivotably attached to the arm member by the stopper ping so as to transmit the seat weight to the stopper pin, wherein the load applied to the stopper pin allows the arm member to rotate about the pivot member so as to produce displacement in a sensor, a bearing structure comprises sleeve members wherein the pivot member is inserted into the arm member via one of the sleeve members while the stopper pin is also inserted into the bracket via the other sleeve member, so that any of part of the insertion holes of the respective sleeve members always comes into contact with the pivot member and the stopper pin, so as not to allow the pivot member and the stopper pin to run freely within the insertion holes when the pivot member and the stopper pin move.
In the bearing structure according to the present invention, part or the entirety of the sleeve member may be tapered so that the sleeve member always comes into contact with the shaft member. Furthermore, part or the entire of the sleeve member may be slit in an axial direction.
Also, in order to cause any of part of the insertion hole of the sleeve member to always come into contact with the shaft member, part or the entirety of the sleeve member may be formed to be bellow-shaped, or part or the entire radial section of the sleeve member may be formed to be polygonal.
In the bearing structure according to the present invention, it is preferable to circumferentially cover a pipe on the shaft member so as to stick on the external surface of the shaft member. In this case, the sleeve member is circumferentially covered on the pipe. Thereby, the clearance between the shaft member and the sleeve member is further reduced, so that abnormal noise due to the rattle of the shaft member during vehicle traveling is further suppressed.
In the bearing structure according to the present invention, the sleeve member may have a double structure comprising an internal sleeve inserted into the insertion hole of the bearing member while being inserted to the shaft member from outside and an external sleeve inserted into the insertion hole of the bearing member while being inserted to the internal sleeve from outside.
A seat-weight measuring apparatus according to the present invention for measuring the seat-weight including the weight of an occupant sitting on a vehicle seat, the seat-weight measuring apparatus comprises a base frame extending in a longitudinal direction of a vehicle, rail brackets respectively arranged toward back and forth ends of the base frame and lying between the base frame and a seat rail which slides in the longitudinal direction of the vehicle, and a sensor section mounted on the base frame and comprising a strain sensor fixed to a central portion of the base frame in a longitudinal direction and arms respectively arranged at back and forth ends of the base frame and extending in the longitudinal direction, the arm having a pressing part for transmitting a force to the strain sensor at one end (a central end) and a connecting part to the rail bracket at the other end (one of the front end and the rear end), wherein the arm and the rail bracket are provided with insertion holes for center-of-rotation pins formed thereon, and the arm and the rail bracket are connected to each other so as to be relatively rotatable about the pin, wherein the seat-weight measuring apparatus further comprises an internal sleeve lying between the insertion hole of the arm and the external periphery of the pin while extending into the insertion hole of the rail bracket, and an external sleeve lying between the external periphery of the internal sleeve and the insertion hole of the rail bracket, and wherein the internal sleeve, while being press-fitted into the insertion hole of the arm, has a pressing section which is elastically pressed onto the external periphery of the pin so as to slidably and elastically keep the pin in contact with the internal sleeve, and wherein the external sleeve, while being press-fitted into the insertion hole of the rail bracket, has a pressing section which is elastically pressed onto the external periphery of the internal sleeve so as to slidably and elastically keep the internal sleeve in contact with the pin.
In addition, by contrast to the above description, the internal sleeve may arranged in the rail bracket side while the external sleeve in the arm side, and this case is also within the scope of the present invention.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed.